The invention relates generally to pick up truck tailgates, and more particularly to a method and apparatus to provide tailgate lift assist.
A pickup truck tailgate must be capable of constraining cargo in the pickup truck box, providing structure to thebox, and in some cases supporting the weight of materials extending beyond the box when the tailgate is open. As a result, the weight of a typical tailgate is substantial. For example, the tailgate of a fill size pickup truck may weigh about 55 tbs.
In addition to the loads ass ociated with constraining and supporting cargo, the tailgate must be capable of withstanding impact loads associated with many thousands of cycles of opening and closing. These loads may be quite significant, particularly those associated with dropping or slamming a heavy tailgate into open position. Cables extending from the D posts to the left and right ends of the tailgate are often employed to support the tailgate in open position. These cables must have sufficient strength and durability to withstand many cycles of dropping or slamming the tailgate into open position.
The weight associated with a tailgate may make the tailgate difficult for some persons to operate, in that the amount of force that must be applied to initiate closing of the tailgate by lifling it from its fully open position is largely dependent on its weight. Similarly, the amount of force required to support the tailgate to prevent it from slamming as it is being lowered into fully open position is dependent on its weight.
The need for a pra ctical and economical tailgate lift assist system for pickup trucks has long been recognized. Ideally, such a system would be suitable for both OEM installation and retrofit installation by dealers and customers, and would facilitate both open ing and closing without adding unacceptable weight and without unduly complicating removal and replacement of the tailgate. Such a system would also be lightweight and capable of economical mass production.
Various proposals have been made over the years to provide tailgate lift assist. U.S. Pat. No. 5,358,301 describes a system that employs a torsion rod mounted within the tailgate. The system is somewhat complicated, and it is believed that the system described in this patent would be difficult to install.
The in vention provi des a tailgate lift assist system and associated me thods and apparatus that provide controlled force at various points as a tailgate is pivoted between open and closed position to assist the operator in both opening and closing the tailgate, and that may be installed without undue difficulty. The system is suitable for commercial mass production, and is preferably suitable for customer, dealer, or OEM installation.
The system includes a tensioning mechanism that preferably comprises one or more springs, bungee cords or other resilient members, and may comprise a plurality of resilient members having different spring constants or stiffness, to provide predetermined levels of assist at various points in opening and closing of the tailgate. In the preferred embodiment, the tensioning mechanism comprises a pair of coil springs in series loaded in tension and extending across the tailgate, and a noise-reducing sheath at least partially covering the coil springs. In other embodiments, the tensioning mechanism may be positioned in other orientations, e.g., diagonally or vertically.
The tensioning mechanism preferably transmits tension between supports, or support members, such as cables, cords, chains or the like to equalize tension in the support members. The tensioning mechanism preferably has two connection points, one for each of two support members on opposite ends of the tailgate, and is configured to provide equal tension to each support member. This may be accomplished by permitting the tensioning mechanism to move in the direction of greater tension in response to any transitory inequality in tension.
During closing, the tensioning mechanism preferably retracts portions of the supports into the interior of the tailgate as the tailgate is pivoted upward, and decreases tension on the supports, thereby decreasing upward assist, as the tailgate is pivoted upward from its fully open position. During opening, the sequence is reversed, with the tensioning mechanism permitting withdrawal of the support members from the tailgate and increasing tension as the tailgate approaches fully open position. During opening, the support tension increases the potential energy of the tensioning mechanism, and during closing, the upward pivoting of the tailgate decreases potential energy.
The support members preferably extend into the interior of the tailgate through openings in the lateral ends of the tailgate. To reduce wear and possible damage due to impacts, reinforcing structures may be mounted on the tailgate walls adjacent the openings to increase the ability of the tailgate. The reinforcing structures may include one or more rollers for engaging the support members in rolling contact instead of sliding contact.
To enable the support members to limit downward pivoting of the tailgate, limiters may be provided on the support members inside the tailgate. Each of the limiters may comprise one or more clamps attaching it to one of the support members, and a resilient, energy absorbing bumper to absorb energy upon impact with one of the reinforcing structures. The bumpers may be made of an elastomeric material.
Installing of a tensioning mechanism often requires provision of a means for maintaining tension on a spring or the like during the installation process, which can increase the time and expense associated with installation. To avoid this problem, the system preferably applies tension to the support members only through a predetermined range of tailgate angles, so that the system may be installed or removed without significant tension on the tensioning mechanism or the support members. That is, when the tailgate is within a certain range of angles, the system is under only minimal tension, such as tension associated with friction and the weight of the support members, and possibly the weight of the tensioning mechanism, which may be regarded as zero tension for purposes of discussion herein.
In the embodiments described in detail below and for which data is presented in the attached drawings, the system applies significant tension to the support members at least when the tailgate is at an angle of between 40 and 90 degrees from its closed position, and the system does not apply significant tension to the support members at least when the tailgate is at an angle of between 0 and 20 degrees from its closed position.
To enable loads to be carried on the tailgate when it is open, e.g., loads associated with elongated items extending beyond the truck bed, without the tailgate pivoting or bouncing upward excessively, the maximum assist provided by the system is preferably well below the minimum force required to initiate upward pivoting under static conditions. For example, in the preferred embodiment, under static conditions, an upward load of at least 10 lbs. in excess of the assist provided by the system must be applied to the tailgate to initiate upward movement from its fully open position.
In the preferred embodiment, the support members are detachably connected to the support members of the pickup truck by small brackets or fittings or the like, held in place by removable and replaceable fasteners such as screws or bolts, and the system does not interfere with removal of the tailgate from the pickup truck after detachment of the support members.
The system is preferably configured so that it does not have any components protruding or visible when the tailgate is closed, When the tailgate is open, its components project only minimally from the tailgate so as to have no adverse impact on clearances or appearance.
The system may be provided as a kit for retrofit installation comprising a tensioning mechanism, new cable assemblies or other supports with limiters preinstalled thereon, reinforcing plates, and fasteners. In some embodiments, the cables may be preattached. In other embodiments, the cables may be attached as part of the installation process. In either case, the kit is preferably configured to enable installation to be accomplished with a relatively small number of steps.
A typical installation process may comprise removing the original cables from the tailgate and D posts, removing a panel from the inner wall of the tailgate, drilling holes if necessary for the new cables and/or reinforcement plates in the end walls of the tailgate, inserting the tensioning mechanism into the interior of the tailgate, installing the reinforcement plates, extending the new cables through the holes, and attaching the cables to the D posts.